The intimate association of virulent bacteria with host cells is generally recognized as an early and critical event in establishing infection. Because little is known about virulence mechanisms of spirochetes, our work is focused on understanding the pathogenesis of spirochetal diseases at the level of bacterium host cell surface interactions. Investigations of the pathogenesis of syphilis are limited by lack of an in vitro growth system for Treponema pallidum. In comparison, growth of the Lyme disease agent, Borrelia burgdorferi, in culture makes this organism attractive for study. Studies in this laboratory indicate that B burgdorferi, like T. pallidum, attaches to and penetrates some eucaryotic cell monolayers. Based on these data and the morphologic and pathogenic similarities between these organisms, it is possible that a generalized mechanism of spirochetal virulence exists. A study of both organisms is, therefore, proposed. In attachment assays with B burgdorferi and human umbilical vein endothelial cells (HUVEC), we have identified four putative borrelial adhesin molecules. Monoclonal antibodies, chromatography, and molecular cloning will be used to isolate these molecules for biochemical and functional characterization. Colonial growth of B. burgdorferi, on solid media will be exploited to 1) define the association between distinct colony morphology and ability to attach to and/or invade HUVEC monolayers, and 2) isolate and create mutants altered in attachment and/or invasion capabilities. The purified adhesins and the mutants isolated will be used in the third project section, which involves an analysis of the characteristics and mechanism of B. burgdorferi and T. pallidum penetration of endothelial tissue. The unique invasive potential of these organisms will be explored using cultured cell systems and excised human umbilical vein segments. These studies will enhance knowledge of spirochetal virulence mechanisms and will provide the basis for further studies on long-range objective, which are to learn 1) the importance of attachment of spirochetes to host cells, 2) how spirochetes pass in and out of the circulation and 3) why and how certain tissues are targeted in disease.